Patent GB-660424-A (GB)
Title: Improvements in or relating to apparatus for indicating the relation between a pre-selected course and the actual course of a mobile vehicle
IPC: G01S1/02
Filed: 1949-05-24
Abstract: 660,424. Radio navigation. CALVERT, R., and WAYNE KERR LABORATORIES, Ltd. May 24, 1950 [May 24, 1949], No. 13783/49. Class 40 (vii). Radio navigation system receiving apparatus comprises a receiver providing two parameters giving the position of the vehicle carrying the receiver, a record of the values of the two parameters corresponding to a selected course, means for determining the difference between each of the actual positional parameters and the corresponding planned parameters represented by the part of the recording medium set against a datum position, and means responsive to the ratio between the two differences for moving the recording medium relative to the datum position to maintain a predetermined ratio so that the movement of the recording medium is representative of the distance travelled along the course and the difference between either of the positional parameters and the corresponding planned parameter is representative of the displacement of the vehicle to one side or the other of the course. The invention is described as a development of that described in Specification 636,180. In the system of that invention the recording medium is driven according to the crossing of the equi-phase contours of one of the patterns providing the parameters so that (Fig. 2) if the record is driven according to the pattern having contours 2 and 3, the recorded course is AB and the craft at P, the record will be set to the position Q on the same contour line 2. Thus the record shows the distance along the course as AQ and not AX where X is the foot of the perpendicular from P to AB. In the present invention with the craft at P the record is driven to indicate the point X. Now the distance # XP=XR cosec XPR in terms of the co-ordinate system 2, 3 and so on, and XP=XG cosec XPG in terms of the co-ordinate system 6, 7 and so on. Introducing constants Kr and Kg relating phase difference to absolute distance over this portion of the patterns which is a constant for a given part of the patterns. If therefore the record is driven such that the ratio of the difference between the recorded and actual values of the two parameters is equal to the above defined constant K for the area in which the craft is then, the record will provide the co-ordinate values of X. Apparatus for carrying out the invention may comprise the record film 10 capable of movement from spool M to spool L under control of a motor D. The film moves past a datum position T at which are arranged reproducers T1, T2, T3 and T4; respectively reproducing from tracks S1, S2, S3, S4. The navigation system receiver Rr feeds values of one of the actual co-ordinates to unit Rm which converts these into angular movement of the shaft 15 corresponding to changes in value. Shaft 16 rotated by unit Rf is likewise moved in response to changes in the value of the corresponding parameter recorded on track S1. The differential Rd coupled to these two shafts rotates the lead-screw 17 in accordance with the difference of the inputs. A similar arrangement comprising units Gg, Gf, Gm and Gd rotates lead-screws 19 in accordance with the difference between the actual value of the other parameter and that recorded on the track S2. Lying perpendicular to the parallel lead-screws 17 and 19 is a further lead-screw 18 controlled by a step-by-step motor Z, on this screw is mounted a pivot carriage C through which slidably passes a metal arm 20 fixed to a pivot E on screw 19. A further carriage F is mounted on screw 17 and when the craft is on course and at the position recorded opposite the datum T, the carriages E, C and F lie along the line of screw 18, a contact on arm 20 touching one on carriage F. So long as these contacts are touching relay J maintains motor D still but it is energized when they part to move the record past the reproducers until contact is again made. The motor Z controls the screw 18 in accordance with the value of K in the above equations which is recorded in track S4 so that for any deviation from course the ratio of the parameter differences is K when the motor D is stationary. A further track S3 on the record provides impulses for a distance indicator H which shows the distance travelled along the track (i.e. AX). The shafts 17 and 19 also control potentiometers R1 and R5, each in bridge circuits, the voltage applied to which through terminals V is controlled by variable resistors R4 and R8. The output of either bridge circuit may be fed over switch W to deviation meter N. According to the position of the switch the meter is controlled to show XP in terms of XR or XG, the constant in the relationship being obtained by the adjustment of R4 or R8. These resistors may be set in accordance with further tracks on record 10, if desired.